In both one-way paging and two-way messaging, duplicate messages may be sent to a selective call device such as a selective call receiver or transceiver for a variety of reasons. A one-way paging system may intentionally be designed to send duplicate messages to create (at the expense of system latency and capacity) greater reliability through time diversity, such as in Motorola's FLEX-TD paging system used in Japan. In each instance, there are several factors that creates complications in the processing of such duplicate messages. For instance, when messages are sent multiple times in an unreliable radio frequency environment, errored characters are received. Most errors are corrected using forward error correction, but some errors are only detected. Other codewords in the message may be so badly corrupted that they correct to the wrong codeword. When a badly corrupted portion of a message corrects to a wrong codeword or character, falsing occurs and detection of duplicate messages becomes a significant problem. In current alphanumeric two-way paging, for example, detected errors are handled in duplicate message processing by negative acknowledging (NACK'ing) errored messages. The negative acknowledgment (NACK) of an errored message creates further channel traffic and thus reduces overall system capacity.
In a two-way messaging environment, a message may be resent to a selective call transceiver (pager) because the message was not delivered well (possibly had too many errors), or an acknowledgment was not received by the two-way messaging system. If a receiver of a message is in a marginal coverage area in a two-way paging environment, messages will likely contain errors. These errors will likely cause a checksum to fail and the message will be negative acknowledged or "NACKed". Repeats of the message are not likely to be any better, particularly for long messages.
Thus, a need exists for a duplicate message processing method and apparatus that recognizes the problem encountered by errored messages and that appropriately handles such duplicate messages by avoiding the unnecessary repeat NACK, display or alerting of such duplicate messages.